Micro-scale impact testing on cemented carbides

In this paper, the mechanical properties of polyurethane foam (PUF) reinforced with glass fiber (RPUF) and non-reinforced PUF were investigated and compared to evaluate their structural applicability and failure criteria. The effects of glass fiber reinforcement were analyzed by tensile, compression, and repetitive impact testing. In the compression test, the differences of compressive response were analyzed by specimen directions, and tensile tests were carried out to evaluate the strain rate sensitivity of two materials in the low strain rate regime (έ<0.1/s). Structural impact tests were carried out using dry drop tests and custom-made equipment. The dimensions of the test PUF specimens were 340 mm × 340 mm × 270 mm. Reaction forces were measured at the bottom of the specimen using impact load sensors with the capacity to measure up to 100 ton. Deformation due to impact load was measured using a high-speed camera system. The time histories of the impact load versus displacement behavior during repetitive impact loading were analyzed. This study presents a comprehensive understanding of the effect of fiber reinforcement on the mechanical behavior of PUF.

Erosion caused by solid particle impact is a very common phenomenon. In many fields such as particle (or slurry) transportation, equipment protection in a dust environment, turbine engineering, etc., prevention of particle erosion is the task. In other applications, it is used as a tool for desirable material removal, surface cleaning, controlled destruction, numerous studies on this subject have been conducted by researchers from many disciplines including physics, material science, mechanics, manufacturing, standardization, etc.. To provide a comprehensive view of the problem of erosion by solid particle impact, a review is conducted based on the literature collected on material subject of erosion by solid particle impact. The reviewed works are limited to ductile material erosion and four categories: erosion mechanism, parametric studies, material removal modeling and simulation modeling.

Effect of Pre-Crystallization Process and Solid Particle Addition on Cocoa Butter Crystallization and Resulting Microstructure in Chocolate Model Systems

In the production and pipeline transport of various fluids, such as oil and natural gas, solid particles may be entrained in the fluid. These particles, commonly consisting of numerous types and sizes of sand, can travel apart from the streamlines of the fluid and impact the surface of the pipe. With time, enough particles may impinge a pipe wall at a sensitive location, such as an elbow or tee, to result in a measurable wall thickness loss. This may ultimately lead to severe erosion damage causing a leak in a pipeline, a dangerous and costly problem. As a result, a pipeline’s service life may often depend on the rate at which a pipe wall is eroded. The erosion rate, or amount of material loss over a certain time period, depends on a large number of factors. The target material, or material experiencing a thickness loss, such as a pipe wall, influences the rate at which damage occurs. Its density, hardness, yield strength, and microstructure combine to present a certain resistance toward erosion occurring from solid particle impact. Furthermore, the solid particle’s diameter, sharpness, and shape will influence its trajectory, speed, and momentum transfer into the target, thereby requiring the analysis of various particle types in predicting erosion. Finally, the carrier fluid being transported through a pipeline will further affect the solid particle’s movement as it approaches the target. As a result, the fluid’s density and viscosity must be carefully considered in particle tracking and erosion analysis. By considering the aforementioned properties of the target, solid particles, and carrier fluid, it is desirable to be able to predict the erosion rate from a single erosion equation. Other factors depending on these properties may be found in this expression, such as particle impact speed and impingement angle at the target. Velocity measurements by way of Laser Doppler Velocimetry (LDV) were made for particles entrained in a viscous liquid traveling in a submerged, direct impingement jet. In an attempt to obtain representative particle impact characteristics during material erosion, data was collected from the nozzle exit to the target surface in order to track fluid and particle velocities prior to impact with a wall. Average particle sizes of 120 and 550 μm were used to represent typical sand sizes, while much smaller particles with an average diameter of 3 μm were utilized in fluid velocity measurements. The carrier fluid viscosity was varied from 1 to 100 centiPoise, while the nozzle flow rate and fluid density were maintained constant. Changes in approach and estimated impingement velocity occurring due to fluid viscosity and particle size are then presented. For the same impingement geometry and flow situations, metal loss erosion measurements have been made by way of an Electrical-Resistance (ER) probe. Oklahoma #1 sand particles with an average diameter of 150 μm were suspended in a viscous carrier fluid at a measured sand concentration. The measured erosion rate and particle velocities at near target wall locations are then compared to observe the effect of viscosity on material erosion and impact speed. Particle tracking and erosion predictions made by Computational Fluid Dynamics (CFD) can then be experimentally validated.

The basic-safety-principle concerning components in German nuclear power plants (NPP) requires a high material quality in terms of characteristic toughness values. For this purpose, at present, notched-bar impact tests are carried out for example for the determination of the brittle fracture transition temperature. Compact tension tests are performed to determine mechanical and technological characteristics such as the fracture toughness, crack initiation, the crack growth. Because of the scattering in the data, the quantification of the failure behavior in the transition zone of the toughness is only possible with restrictions. Therefore considerably high safety margins are asked for in the design to avoid failure behavior. So far, the crack growth can only be determined in standardized bending tests and requires partial load relief cycles observing the development of the crack opening displacement by a clip-gauge. The time of the crack initiation can be determined with additional time-consuming microscopic analyses of the crack surface after the bending test. The additional instrumentation of the mentioned tests with NDT should provide further information about the failure process and a more precise and reliable determination of the failure probability. In order to document the principle feasibility, three point bending tests and drop impact tests were carried out using SE(B) samples with several nondestructive sensors applied. These sensors are Electromagnetic Acoustic Transducers (EMATs) to record the ultrasonic time of flight (TOF) of an ultrasonic wave travelling around the crack, and Giant Magnetoresistance (GMR) sensors to measure magnetic flux leakage (MFL) signals emanating from the crack. It was shown that both TOF and the MFL provide information about the crack growth during the bending test. In particular, the TOF was shown to increase with the crack length, thus allowing the determination of the crack length without the partial load relief cycles that were needed before. During the drop impact tests, the high-speed acquisition of MFL signals resolved details of the crack formation process.

Studies on solid particle erosion by HVOF sprayed 25% (Cr3C2-25 (Ni20Cr)) + 75% NiCrAlY on Ti-31

The fracture toughness plays a significant role in the structural integrity assessment of reactor pressure vessels (RPVs) in service temperature. The Charpy V-notch (CVN) impact test is used to estimate fracture toughness (KIC or KJIC) indirectly since universal fracture toughness tests are costly, sophisticated and frequently invalid. In this study, a modified correlation which based on the typical model of KJIC-CVN at the upper shelf was established for Chinese SA508-III steel. Thereinto, the effect of test temperature (T) was directly considered in the correlation. To assess the accuracy of fracture toughness when calculating from the value of Charpy-V notch impact energy by using the modified correlation, both the Charpy-V notch impact tests and fracture toughness tests for Chinese SA508-III steel were conducted at different temperatures (100 °C, 150 °C, 200 °C, 250 °C and 320 °C). The results showed that the modified correlation exhibited the high precision for estimating fracture toughness of Chinese SA508-III steel and the relative error for tested and estimated results is within 8%, which is lower than that of other correlations.

Experimental study and visualization of impacting spherical hydrophobic particles on an air – Liquid interface: Newtonian and Boger liquid analysis

The research results of the structured surface relief parameters and properties influence on the blade steel resistance to solid or liquid particles impacts

Previous studies of the Charpy impact test using instrumented pendulum or anvil with V-noteh steel specimens are reviewed. It is concluded that such results add little to the usefulness of the test since even cleavage fractures are normally well beyond yield. No fracture toughness index emerges other than the simple measure of energy from the pendulum. In a second generation of work, fatigue cracked and side grooved (fcsg) specimens promoted below yield fractures up to about the 50 percent fracture appearance transition temperature (fatt). These results have been analysed by linear fracture mechanics to give the dynamic fracture toughness KID. In this interpretation understanding of the oscillations in load records due to specimen vibration is important. Results are discussed in the light of recent studies including an analog model with which near quantitative agreement is found. An improved simple correction factor for inertia loading effects is presented. It is concluded from both this work and supporting measurements of KID by other techniques that dynamic fracture toughness KID can be measured for low-strength steels using the instrumented fcsg impact test subject to the precautions and corrections discussed. Typical values of KID for mild steel are 60 ksi √in. at 0 C falling to 30 ksi √in. at -60 C. The significance of these low values in relation to the much higher static toughness is discussed briefly.

Earlier Charpy V-notch (CVN) specimens were used to determine the nil ductility temperature (NDT) with the help of the impact test. NDT is the measure of embrittlement of material at temperature scale. CVN energy is gross energy supplied to the specimen which includes fracture energy, energy loss due to friction and inertia. So, CVN energy is not a proper characterization of fracture behavior. Thus, the determination of fracture toughness is required. Fracture toughness can be evaluated from quasi-static loading as well as dynamic loading conditions. Fatigue pre-cracked Charpy V-notch (PCVN) specimens are used to find dynamic fracture toughness. Dynamic fracture mechanics differs from quasi-static fracture mechanics in three complex features: rate-dependent material properties, the effect of inertia and reflected stress wave. To overcome the effect of inertia and stress waves, the evaluation of dynamic fracture toughness needs some special technique. In this study, two different methods are used to evaluate the dynamic fracture toughness, one is impact response curve method and another is the J-integral method. For impact response curve method, there is no time constraint present at calculation process but for the J-integral method, there is some condition regarding fracture time to be satisfied to get the valid dynamic fracture toughness data. In this work, Pre-cracked Charpy V-notch (PCVN) specimens of 20MnMoNi55 low-carbon reactor pressure vessel steel are used for impact testing in Pendulum testing machine and Drop weight machine for 7 different velocities ranging from 1 m/s to 9 m/s at cryogenic temperature (−70 °C). Calibration between the test results from the impact test on pendulum type and Drop weight test is done and found to be matching. Dynamic fracture toughness at each velocity is evaluated and compared using two different methods namely impact response curve method and J-integral method. Based on the results found, it is observed that two methods yield the same results if the time constraint referred is maintained for J-integral method.

Nowadays, in various industries, in particular in nuclear energy, to determine the fracture toughness, along with standard tests of compact specimens, which are quite expensive and complex, methods are developed to determine these characteristics by impact tests of Charpy specimens using different correlations between Charpy impact fracture energy (CVN) and critical stress intensity factor (J-integral). The paper analyzes correlation and analytical methods, the authors of which consider them universal for a certain class of steels. Correlation methods are divided into one-stage and two-stage. One-stage methods allow to obtain the value of the critical stress intensity factor by the known fracture energy. Two-stage methods in the first stage offer the calculation of the dynamic critical stress intensity factor, in the second the temperature shift and obtaining a static critical stress intensity factor. Analytical methods according to the іmpact fracture diagram of the specimen allow to construct a J-R curve and calculate the value of the J-integral. A series of fracture tests of CT specimens made of heat-resistant steel 22K was carried out, the reference temperature T0 was determined according to the single-temperature method of the ASTM-1921 standard and the Master curve was constructed. A series of standard Charpy specimens impact tests in the temperature range -50…+100°С was performed using an instrumented drop-weight impact testing machine equipped with a high-speed registration system. According to the results of Charpy specimens impact tests, the fracture toughness were determined using different methods. It is established that both analytical and correlation methods cannot be universal and can be used to determine the fracture toughness of 22K steel. Therefore, a new exponential correlation was proposed between the fracture energy of the Charpy specimens and the critical stress intensity factor for heat-resistant steel 22K.

Surface strength: definition and testing by a sand impact method

The effect of neutron radiation on the fracture characteristics of an A533 Grade B Class 1 pressure vessel steel was investigated using standard and instrumented precracked Charpy impact tests. Use of the instrumented impact test with precracked specimens has allowed fracture toughness values to be determined from the Charpy test. Neutron exposure resulted in minute decreases in the upper-shelf Charpy energy and fracture toughness, and an increase in the ductile brittle transition temperature (DBTT). The Charpy transition temperature shifted about 29 K while the fracture toughness shift was about 20 K. The temperature variation of the dynamic yield strength exhibited dips at DBTT for both unirradiated archive and irradiated materials.

Abstract— The criteria for determining whether ferritic material exhibits fully ductile behaviour are generally based on the fracture toughness vs temperature relationship determined from standard laboratory test pieces (e.g. Charpy V Impact tests or fracture toughness specimens). This relationship defines a ductile‐brittle transition region. When fully ductile, microvoid coalescence behaviour is experienced, and fracture toughness is described as being on the “upper shelf”. At “off the shelf” temperatures brittle, cleavage fracture is experienced. On the lower shelf the material is entirely brittle, exhibiting 100% crystallinity on the fracture face. As the temperature increases, initiation of tearing by microvoid coalescence occurs and some stable tearing can occur prior to the cleavage event. Material toughness increases with temperature until the upper shelf condition is achieved.The characteristics of fracture toughness tests in terms of the toughness level exhibited and the extent of ductile tearing experienced have been used as a guide to whether the structural application (e.g. a pressure vessel) will behave in a brittle or a ductile manner. This paper reports on a feasibility study where various worked examples have been performed to examine the concept of using a “cut off” on the failure assessment diagram, determined from the conditions required to cause plastic collapse of a pressure vessel, as a criterion for defining effective “ductile” operation. Fracture assessment procedures (R6 revisions 2 and 3 and PD6493 levels 2 and 3) have been utilised to determine the influence on pressure vessel performance of the behaviour of fracture toughness test specimens.The procedure of plotting a structural collapse “cut off” on a failure assessment diagram enables the assessment of whether a particular flaw geometry would result in gross deformation of the structure at failure. The use of this procedure provides an unambiguous demarcation between “fracture dominated” and “collapse controlled” conditions. This procedure facilitates judgements on the level of toughness necessary to ensure ductile operation and whether a “tearing plus toughness” requirement is necessary.It is recommended that consideration be given to including structural collapse into fracture assessment procedures carried out using R6 revision 3 or PD 6493:1991 procedures in order to determine the conditions when enhanced toughness no longer influences structural performance (i.e. when effective “upper shelf” conditions are attained).